The formation and deposition of iron sulfide scaling products inhibits or blocks hydrocarbon migration pathways, ultimately reducing production, and causes severe corrosion and equipment damage to both upstream and downstream facilities. As used here, “iron sulfide” and “iron sulfides” refers to compounds including iron and sulfur in various proportions, such as mackinawite (FeS), pyrrhotite (Fe(1-x)S), greigite (Fe3S4), marcasite (FeS2 polymorph), and pyrite (FeS2). Iron sulfide scaling in sour petroleum systems is often ignored because of the difficulty in preventing its formation through nucleation, aggregation, and large scale build-up of iron sulfide minerals according to the transformation shown in Reaction (1).Fe2++H2S(aq)→FeS(aq)→Mackinawite (FeS)→Pyrrhotite (Fe1-xS)→Greigite (Fe3S4)→Marcasite (FeS2 polymorph)→Pyrite (FeS2)   (1)Scaling removal techniques typically used to restore reservoir productivity in oil and gas fields include conventional chemical and mechanical techniques. However, the mechanical cleaning techniques are very expensive, entail laborious processes, and do not adequately remove most of the stable iron sulfide scaling products (such as Fe3S4(greigite), FeS2(marcasite) and FeS2(pyrite)) that are directly in contact with downhole wellheads and pipelines. Moreover, some cleaning processes can cause abrasive wear to production metal coatings without restoring the permeability that has been lost in downhole producing zones.
Aqueous acid chemical removal methods have been recognized to reduce some iron sufide scaling products (such as FeS(mackinawite) and Fe(1-x)S(pyrrhotite)) in the petroleum industry. However, laboratory and pilot plant data show that upon contact with iron sulfide scaling products, these acidic solvents release hydrogen sulfide (H2S), free-floating iron sulfides, and sulfur intermediate species that undergo oxidation into sulfate and other components that are less readily dissolved by acidic solutions. The released hydrogen sulfide is hazardous and poses a health threat to oilfield workers, and the free-floating iron sulfides lead to additional scaling, formation damage, and corrosion problems in oil and gas fields. In addition, the oxidized sulfur intermediates are much less readily dissolved by acidic solutions than the iron sulfides.